The present invention relates to a lubrication system, particularly for the lubrication of internal combustion engines, to provide improved fuel economy and fuel economy retention.
With environmental standards becoming more strict, the ability to provide fuel economy is an important requirement for modern engine oils. Additives that have been used or proposed for this purpose include oil-soluble organo-molybdenum compounds and organic friction modifiers such as esters. Such additives provide improved initial fuel economy, to a greater or lesser extent. However, they tend to lose their effectiveness over time due to the deterioration of the engine oil during service. Recently, in addition to fuel economy performance of fresh oil, retention of fuel economy over an extended period has been given increasing attention in the industry. Therefore more effective additives are now required to provide both improved fuel economy and fuel economy retention.
Oil-soluble esters are one well-known group of additives that may enhance fuel economy performance. In general, these esters are able to provide good lubricity between sliding surfaces. The polar moieties of the molecules assist them to adsorb to metal surfaces, resulting in reduced metal-metal contact. There are many references on the use of esters and/or modified esters, e.g., sulphurised esters, to improve fuel economy. Examples include the esters described in EP-A-0853100, EP-A-0649459, WO-A-93/21288, EP-A-0206748, U.S. Pat. No. 4495088, U.S. Pat. No. 4243538 and U.S. Pat. No. 4289635. Further examples of ester lubricity additives and their use in lubricant compositions are disclosed in U.S. Pat. No. 4175047, U.S. Pat. No. 4879052 and WO 96/01302. These latter references describe esters which are groups of adipate and so-called xe2x80x9cpolyol-estersxe2x80x9d that are derivatives of alcohols with 2 to 4 hydroxyl groups (xe2x80x94OH).
The present invention provides a novel approach to the problem of improving fuel economy and fuel economy retention, by providing a binary liquid system comprising two substantially immiscible liquid phases. More specifically, the present invention provides a lubrication system comprising
a) a first liquid phase comprising a base oil having a kinematic viscosity at 100xc2x0 C. (KV100) in the range from 2 to 100 cSt, and
b) a second liquid phase comprising a polar organic liquid that is substantially immiscible with said first liquid phase
As used herein, the expression xe2x80x9cbinary liquidxe2x80x9d, means a composition that comprises two substantially immiscible liquid phases. That is, it settles to form two separate liquid phase s, as distinguished from an emulsion or dispersion in which one phase is distributed through the other.
The base oil employed in the composition according to the invention may be any of the conventionally used lubricating oils and is preferably a mineral oil, a synthetic oil or a mixture of mineral and synthetic oils. Mineral basestocks can be any conventionally refined basestocks, for instance solvent refined, hydrotreated, or isomerised, e.g., wax-isomerised, basestocks. Synthetic basestocks that may be used include poly-olefin, polybutene, alkylbenzene, esters, silicone oils, etc.
The base oil preferably has a KV100 of from 3 to 50 cSt, more preferably from 4 to 10 cSt.
Preferably, the second liquid phase comprises an ester of a polybasic acid or anhydride thereof, preferably a dicarboxylic acid, and an alcohol which is polyol alcohol or a mixture of polyol and monohydric alcohols, preferably a mixture of a polyol and a monohydric alcohol. The polyol is preferably branched. More preferably, the second liquid phase comprises a complex alcohol ester that is the reaction product of a polyol of the general formula
R(OH)n
wherein
R is an aliphatic or cyclo-aliphatic hydrocarbyl group having 2 to 20 carbon atoms and n is at least 2,
a polybasic acid or an anhydride thereof provided that the ratio of equivalents of said polybasic acid to equivalents of alcohol from said polyol is in the range from 1.6:1 to 2:1, and
a monohydric alcohol, provided that the ratio of equivalents of said monohydric alcohol to equivalents of said polybasic acid is in the range from 0.84:1 to 1.2:1;
wherein said complex alcohol ester exhibits a pour point of less than or equal to xe2x88x9220xc2x0 C., and a viscosity in the range from 100 to 700 cSt at 40xc2x0 C.
Preferably, the polyol is selected from neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, monopentaerythritol, di-pentaerythritol and mixtures thereof, and is preferably trimethylolpropane. The dibasic acid or anhydride has preferably 2 to 12 carbon atoms. It can be selected from adipic, azelaic, sebacic and dodecanedioic acids, succinic anhydride, glutaric anhydride, adipic anhydride, maleic anhydride, phthalic anhydride, nadic anhydride, methylnadic anhydride, hexahydrophthalic anhydride and mixed anhydrides of polybasic acids. Preferably the monohydric alcohol has 5 to 13 carbon atoms, more preferably it has 10 carbon atoms.
Preferred complex esters comprise the polyol, the polybasic acid or anhydride, and the monohydric alcohol in a ratio of substantially 1:3:3, or substantially 1:3:2.
Information as to the manufacture of such complex alcohol esters may be found in WO 98/10040, WO 98/10041 and WO 98/45389. These esters are generally known as complex alcohol esters (CALE). Initially, attempts were made to find methods of solubilizing various forms of CALE, because of its low solubility in engine oils. It has surprisingly been found, however, that a two-phase system with engine oil as the first phase, and a CALE as the second phase, although the phases are essentially immiscible, provides an engine oil that exhibits both improved fuel economy and fuel economy retention.
The complex alcohol esters with the above mentioned ratios 1:3:3 and 1:3:2 respectively have the stylised structures (A) and (B) respectively. 
In these formulae, D represents an alkyl group derived from the monohydric alcohol, A represents of the acid moiety, and T represents the group derived from the polyol. n represents the number of repeating units, and the esters are typically mixtures with n being from 1 to 3.
As used in the Examples below, CALE typically has the following properties:
KV100 5-100 cSt, more preferably 10-60 cSt, most preferably 15-20 cSt
VI 80-180, preferably 100-160, most preferably 120-150
Because of their relatively high molecular weight, which is preferably in the range of 500 to 1500, and with the preferred esters of formula (A), having molecular weights from 700 to 1100, the complex alcohol esters are used as mixtures of the complex ester of formula A or of formula B, with a diluent, which can be conveniently an ester of a dicarboxylic acid and a monohydric alcohol, such as diisodecyl diadipate (DIDA) or ditertiary decyl adipate (DTDA). Diisodecyl phthalate, or other solvents, may be used if desired. The proportion of complex alcohol ester to diluent is preferably from 10:1 to 1:10 by volume, more preferably from 5:1 to 1:5 and especially from 2:1 to 1:1 by volume.
The diluent is used in the mixture because undiluted CALE of the operable molecular weight range is too viscous for convenient handling. It is found that when the diluted CALE is mixed with the engine oil, the CALE, with a minor proportion of the diluent, separates as the lower phase, with the major proportion of the diluent passing into the upper phase of engine oil.
Thus in another aspect the invention provides a lubrication system comprising:
(a) a first liquid comprising a base oil having a KV100 of from 2 to 100 cSt, and
(b) a second liquid comprising a polar organic liquid and a diluent, the polar organic liquid being substantially immiscible with the first liquid such that when the two liquids (a) and (b) are mixed they settle to form a two-phase liquid comprising a first phase that is rich in the said base oil and a second phase that is rich in the said polar organic liquid. The said diluent may be present in both the first and second phases.
Conveniently the diluent selected is the same as the solvent that is used in the preparation of the CALE, for example the diluent is DIDA or DTDA. Thus the method for preparing the CALE can provide a ready-diluted product without the need to add further diluent before the CALE is incorporated into the lubrication system of the present invention.
The lubrication system according to the present invention may contain one or more conventional lubricant additives as are well known to the person skilled in the art. The actual additives selected will depend on the intended application of the lubricant, but typically will include one or more of viscosity index (xe2x80x98VIxe2x80x99) improvers, pour point depressants, detergents, dispersants, antioxidants, antiwear agents, corrosion inhibitors, antifoam agents, other friction modifiers and the like. The VI improver, detergent and dispersant are each preferably included in an amount from 0.5 to 10 wt % based on the total weight of the lubricant composition. The other additives are each preferably included in an amount from 0.01 to 5 wt % based on the total weight of the lubricant composition. These additive treat levels refer to the amount of active ingredients, i.e., the actual additive component, and do not include any diluent or carrier fluid. These additives may be dissolved or dispersed into either the first, base oil phase or the second, organic polar liquid phase, or may be distributed across both phases. Preferably, however, the additives are incorporated into the first, base oil phase. Indeed an advantage of the present invention is that the immiscible organic polar liquid phase may be combined with an already formulated lubricant, e.g., a fully formulated engine oil. The improvement in fuel economy and fuel economy retention benefit brought by the immiscible polar organic liquid appears to be largely independent of the nature of the base oil and lubricant additive s selected for the major portion of the lubrication system.
Thus in a further aspect the present invention provides a lubrication System comprising:
(a) a first liquid phase comprising fully formulated lubricant composition, and
(b) a second liquid phase comprising a polar organic liquid that is substantially immiscible with said first liquid phase.
Preferably the first liquid phase is a fully formulated crankcase lubricant suitable for use in an internal combustion engine.
The present invention also provides the use of a composition as described herein in lubricating an engine to improve fuel economy, and/or to improve fuel economy retention.
The present invention also provides a method of lubricating an internal combustion engine which comprises adding to the engine a lubricant composition as defined above. In this method, phases (a) and (b) can be combined before they are added to the engine, they can be added to the engine simultaneously, or they can be added to the engine sequentially.
Where CALE is used in a single blend, which includes the ester [a], base oil [b] and additives [c] together, this composition exhibits higher fuel economy than does a mixture of [b] and [c], which is the conventional engine oil composition. The CALE content may be 1 to 30% by weight based on the total weight of the mixture of [a], [b] and [c], preferably, 1 to 20%, more preferably 5-10% by weight.
Where CALE is added separately, with [a] being added to the engine after the mixture of [b] and [c], immediately or after a certain period, the fuel economy is surprisingly improved after addition of [a]. The amount of CALE may be 1 to 30% by weight, based on the total weight of the final mixture of [a], [b] and [c], preferably 1 to 20%, by weight more preferably 5-10% by weight. In addition, it has been found that this improved fuel economy may be retained for a duration equivalent to at least 10,000 miles.
Where an engine is treated with [a], before being filled with a mixture of [b] and [c], so that CALE is added in a manner analogous to flushing oil, or pre-treatment oil for flushing or break-in, the CALE is believed to coat the metal surface, leading to lower friction and reduced wear. Thus, this modified surface is responsible for improved fuel economy and wear-protection for a long service period compared to the operation without CALE treatment. The preferred amount of [a] for this purpose may be 50 to 100% by weight based on the weight of oil required in the engine specification.
A further embodiment of the invention provides a method of lubricating an internal combustion engine which comprises adding to the engine a polar organic liquid, operating the engine, and subsequently adding to the engine a lubricating oil having a KV100 in the range from 10 to 100 cSt, the polar organic liquid and the lubricating oil being substantially immiscible. If desired, the polar organic liquid is drained from the engine before addition of the lubricating oil. It is found that the effect of adding the polar organic liquid persists for an extended period, compared with using the lubricating oil alone.